I have multiple tables with different column names like below,
customer table:
c_id,
customer_name,
phone_number,
postal_code
Employee Table: Employee_name, e_id, mobile_no,zip_code
student Table: s_id, student_name, post_code
I need to create view to combine those tables like below
User Table: userId (c_id, e_id, s_id), userName (all name columns), zip_code, contact
Sample Data
Customer Table:
| c_id | Company_Name | Phone |
|----------------------------------|
| 1 | Company 1 | *******|
|----------------------------------|
Employee Table:
| e_id | Employee_Name | Mobile |
|----------------------------------|
| 1 | employee 1 | *******|
|----------------------------------|
Expected View:
| userId | user_Name | contact |
|-------------------------------------|
| c_1 | Company 1 | ******* |
|-------------------------------------|
| e_1 | employee 1 | ******* |
|-------------------------------------|
how to create the view please help me, Thanks in advance
just use Union or Union All depending on duplicate values. based on data
CREATE VIEW view_name
AS
SELECT concat('c_',c_id) AS userId,
company_name AS user_Name,
phone AS contact
FROM customer
UNION
SELECT concat('e_',e_id),
employee_name,
mobile
FROM employee
dbfiddle
based on tables
CREATE VIEW view_name
AS
SELECT c_id AS userId,
customer_name AS userName,
postal_code AS zip_code,
phone_number AS contact
FROM customer
UNION
SELECT e_id,
employee_name,
zip_code,
mobile_no
FROM employee
UNION
SELECT s_id,
student_name,
post_code,
NULL
FROM student
Related
I have 3 tables : employee, event, and these are N-N so the 3rd table employee_event.
The trick is, they can only N-N within the same group
employee
+---------+--------------+
| id | group |
+---------+--------------+
| 1 | A |
| 2 | B |
+---------+--------------+
event
+---------+--------------+
| id | group |
+---------+--------------+
| 43 | A |
| 44 | B |
+----
employee_event
+---------+--------------+
| employee_id | event_id |
+-------------+--------------+
| 1 | 43 |
| 2 | 44 |
+---------+--------------+
So the combination employee_id=1 event_id=44 should not be possible, because employee from group A can not attend an event from group B. How can I secure my DB with this?
My first idea is to add the column employee_event.group so that I can make my two FK (composite) with employee_id + group and event_id + group respectively to the table employee and event. But is there a way to avoid adding a column in the join table for the only purpose of FKs?
Thx!
You may create a function and use it as a check constraint on table employee_event.
create or replace function groups_match (employee_id integer, event_id integer)
returns boolean language sql as
$$
select
(select group from employee where id = employee_id) =
(select group from event where id = event_id);
$$;
and then add a check constraint on table employee_event.
ALTER TABLE employee_event
ADD CONSTRAINT groups_match_check
CHECK groups_match(employee_id, event_id);
Still bear in mind that rows in employee_event that used to be valid may become invalid but still remain intact if certain changes in tables employee and event occur.
Assume we have the following table whose purpose is to autogenerate a numeric id for distinct (name, location) tuples:
CREATE TABLE mapping
(
id bigserial PRIMARY KEY,
name text NOT NULL,
location text NOT NULL,
);
CREATE UNIQUE INDEX idx_name_loc on mapping(name location)
What is the most efficient way to query for a set of (name, location) tuples and autocreate any mappings that don't already exist, with all mappings (including the ones we created) being returned to the user.
My naive implementation would be something like:
SELECT id, name, location
FROM mappings
WHERE (name, location) IN ((name_1, location_1)...(name_n, location_n))
do something with the results in a programming language of may choice to work out which results are missing.
INSERT
INTO mappings (name, location)
VALUES (missing_name_1, missing_loc_1), ... (missing_name_2, missing_loc_2)
ON CONFLICT DO NOTHING
This gets the job done but I get the feeling there's probably something that can a) be done in pure sql and b) is more efficient.
You can use DISTINCT to get all possible values for the two columns, and CROSS JOIN to get their Carthesian product.
LEFT JOIN with the original table to get the actual records (if any):
CREATE TABLE mapping
( id bigserial PRIMARY KEY
, name text NOT NULL
, location text NOT NULL
, UNIQUE (name, location)
);
INSERT INTO mapping(name, location) VALUES ('Alice', 'kitchen'), ('Bob', 'bedroom' );
SELECT * FROM mapping;
SELECT n.name, l.location, m.id
FROM (SELECT DISTINCT name from mapping) n
CROSS JOIN (SELECT DISTINCT location from mapping) l
LEFT JOIN mapping m ON m.name = n.name AND m.location = l.location
;
Results:
DROP SCHEMA
CREATE SCHEMA
SET
CREATE TABLE
INSERT 0 2
id | name | location
----+-------+----------
1 | Alice | kitchen
2 | Bob | bedroom
(2 rows)
name | location | id
-------+----------+----
Alice | kitchen | 1
Alice | bedroom |
Bob | kitchen |
Bob | bedroom | 2
(4 rows)
And if you want to physically INSERT the missing combinations:
INSERT INTO mapping(name, location)
SELECT n.name, l.location
FROM (SELECT DISTINCT name from mapping) n
CROSS JOIN (SELECT DISTINCT location from mapping) l
WHERE NOT EXISTS(
SELECT *
FROM mapping m
WHERE m.name = n.name AND m.location = l.location
)
;
SELECT * FROM mapping;
INSERT 0 2
id | name | location
----+-------+----------
1 | Alice | kitchen
2 | Bob | bedroom
3 | Alice | bedroom
4 | Bob | kitchen
(4 rows)
I have 2 tables that I need to join based on distinct rid while replacing the column value with having different values in multiple rows. Better explained with an example set below.
CREATE TABLE usr (rid INT NOT NULL AUTO_INCREMENT PRIMARY KEY,
name VARCHAR(12) NOT NULL,
email VARCHAR(20) NOT NULL);
CREATE TABLE usr_loc
(rid INT NOT NULL AUTO_INCREMENT PRIMARY KEY,
code CHAR NOT NULL PRIMARY KEY,
loc_id INT NOT NULL PRIMARY KEY);
INSERT INTO usr VALUES
(1,'John','john#product'),
(2,'Linda','linda#product'),
(3,'Greg','greg#product'),
(4,'Kate','kate#product'),
(5,'Johny','johny#product'),
(6,'Mary','mary#test');
INSERT INTO usr_loc VALUES
(1,'A',4532),
(1,'I',4538),
(1,'I',4545),
(2,'I',3123),
(3,'A',4512),
(3,'A',4527),
(4,'I',4567),
(4,'A',4565),
(5,'I',4512),
(6,'I',4567);
(6,'I',4569);
Required Result Set
+-----+-------+------+-----------------+
| rid | name | Code | email |
+-----+-------+------+-----------------+
| 1 | John | B | 'john#product' |
| 2 | Linda | I | 'linda#product' |
| 3 | Greg | A | 'greg#product' |
| 4 | Kate | B | 'kate#product' |
| 5 | Johny | I | 'johny#product' |
| 6 | Mary | I | 'mary#test' |
+-----+-------+------+-----------------+
I have tried some queries to join and some to count but lost with the one which exactly satisfies the whole scenario.
The query I came up with is
SELECT distinct(a.rid)as rid, a.name, a.email, 'B' as code
FROM usr
JOIN usr_loc b ON a.rid=b.rid
WHERE a.rid IN (SELECT rid FROM usr_loc GROUP BY rid HAVING COUNT(*) > 1);`
You need to group by the users and count how many occurrences you have in usr_loc. If more than a single one, then replace the code by B. See below:
select
rid,
name,
case when cnt > 1 then 'B' else min_code end as code,
email
from (
select u.rid, u.name, u.email, min(l.code) as min_code, count(*) as cnt
from usr u
join usr_loc l on l.rid = u.rid
group by u.rid, u.name, u.email
) x;
Seems to me that you are using MySQL, rather than IBM DB2. Is that so?
I got a key-value based table where each key-value pair is assigned to an entity which is identified by an id:
|_id__|_key_______|_value_|
| 123 | FIRSTNAME | John |
| 123 | LASTNAME | Doe |
And I want to transform it a structre like this:
|_id__|_firstName_|_lastName_|
| 123 | John | Doe |
I suppose one can use postgres build in crosstab function to do it.
Can you show me how to do it and explain why it works?
First of all activate the build in tablefunc-extension:
CREATE EXTENSION tablefunc;
Then create table and add sample data:
CREATE TABLE example (
id int,
key text,
value text
);
INSERT INTO example VALUES
(123, 'firstName', 'John'),
(123, 'lastName', 'Doe');
Now lets prepare the crosstab statment:
SELECT *
FROM example
ORDER BY id ASC, key ASC;
Its important to have the ORDER BY here.
Result:
|_id__|_key_______|_value_|
| 123 | FIRSTNAME | John |
| 123 | LASTNAME | Doe |
Solution
Now crosstab creates the table as we want:
SELECT *
FROM crosstab(
'SELECT *
FROM example
ORDER BY id ASC, key ASC;'
) AS ct(id INT, firstname TEXT, lastname TEXT);
Result:
|_id__|_firstName_|_lastName_|
| 123 | John | Doe |
How it works #1
To however understand how it works I found it easiest to just change the ORDER BY and see what happens:
SELECT *
FROM crosstab(
'SELECT *
FROM example
ORDER BY id ASC, key DESC;'
) AS ct(id INT, firstname TEXT, lastname TEXT);
Result:
|_id__|_firstName_|_lastName_|
| 123 | Doe | John |
As we changed the sorting of the key, the crosstab function sees the keys sorted in the other direction, thus reversing the generated columns.
How it works #2
Another thing that helped me understand how it works: the column definition is all about positions:
SELECT *
FROM crosstab(
'SELECT *
FROM example
ORDER BY id ASC, key ASC;'
) AS ct(blablafirst INT, blablasecond TEXT, blablathird TEXT);
Result
|_blablafirst__|_blablasecond_|_blablathird_|
| 123 | John | Doe |
I am new to postgresssql.
I have two table like this
Table A
id |value | type1 | type2 | type3
bigint |text | bigint | bigint | bigint
Table B
Id | description
bigint | text
Table A's type1,type2,type3 is the ids of Table B but not foreign key constraint.
I have to retrieve like this
Select a.id,
a.value,
b.description1(as of a.type1),
b.description1(as of a.type1),
b.description1(as of a.type1)
If you have to many columns you should consider change your db design
TableA
id | value
1 | <something>
2 | <something>
TableAType
id | TableA.id | type_id | typeValue
1 | 1 | type1 | bigint
2 | 1 | type2 | bigint
3 | 1 | type3 | bigint
.....
4 | 1 | typeN | bigint
TableB (type_description)
Id | description
bigint | text
Then your query become more simple and isn't affected when you add/remove types.
SELECT TB.Description, TT.TypeValue
FROM TableAType TT
JOIN TableB TB
ON TT.Type_id = TB.id
Then you can use a PIVOT to get the tabular data. Again the advantage is you can delete remove types, and your query doesnt change, only need update the types tables.
You should (LEFT) JOIN tableB 3 times, and use a different alias for each one.
select id, value,
type1, t1.description descri1,
type2, t2.description descri2,
type3, t3.description descri3
from tableA ta
left join tableB t1
on ta.type1 = t1.id
left join tableB t2
on ta.type2 = t2.id
left join tableB t3
on ta.type3 = t3.id;